John Singleton, we hardly knew ye. Long gone is the 23-year-old upstart who bravely challenged our collective thirst for righteous, revenge-motivated bloodshed with his brilliant debut feature, “Boyz N the Hood” (1991).

The new Singleton — exemplified by such ghetto folk-hero sagas as “Baby Boy” and “Shaft” — embraces urban violence like a once-idealistic politician embraces pork barrels, specifically by exploring circumstances under which one man may justifiably “pop a cap” into another.

Suffice to say, caps are popped like nobody's business in “Four Brothers,” a lusty tale of revenge about four adoptive brothers who scour the blighted wilderness of modern-day Detroit to find the villains who killed their mother.

Fixated on the carnage, Singleton forgets to foster suspense, leaving us with a morally hollow and dramatically unfulfilling affair that resorts to silliness — a violence-engorged payback farce. The movie's one saving grace is an appealing if largely unexplored theme of interracial kinship.

Gunned down in an apparent convenience store robbery, saintly social worker Evelyn Mercer (Fionnula Flanagan) is mourned by her four adoptive sons. The eldest, Bobby (Mark Wahlberg), is a roughneck with a spotty criminal record. Jeremiah (hip-hop star André Benjamin, in a surprisingly polished performance) is an ex-union agitator now on the straight and narrow. Sleek ladies’ man Angel (Singleton regular Tyrese Gibson) washed out of the Marines, and Jack — the baby of the bunch, played by former Valley resident Garrett Hedlund (“Troy”) — is an aspiring punk rocker with more attitude than talent.

Evelyn raised no angels, but the Mercer boys are “congressmen compared to what they could have been” had she not plucked them out of an ineffective foster care system, according to Lt. Green (Terrence Howard from “Hustle and Flow”), the veteran detective investigating her murder.

While the official investigation stalls, the brothers Mercer delicately conduct their own inquiries, uncovering proof that their do-gooding mother wasn't killed randomly, but assassinated by gangster warlords and venal politicians. Penned by screenwriters David Elliot and Paul Lovett, “Four Brothers” owes a healthy creative debt to the John Wayne/Dean Martin cowboy thriller “The Sons of Katie Elder” (1965).

Using the inner city — with its spurious land development schemes, gangsters and impotent police — as a surrogate for the Old West is a good idea that subtly malfunctions in “Four Brothers.” There's something about the way Bobby and his siblings run roughshod over their old neighborhood — brandishing weapons at basketball games, trading gunfire in apartment buildings and smashing up whole blocks of parked vehicles in their pursuit of the murderers — that strikes the viewer as too lawless, even by Detroit standards. As Green, Howard takes law enforcement obliviousness to Clouseau-like extremes.

Even more distressing, Singleton appears to have lost the ability to create emotionally realistic moments. Wahlberg's brief crying jag in the film's early moments feels staged and moodless, and a series of perfunctory flashback images involving Evelyn's motherly bromides fails to provide the story with the rich sentimental foundation it needs.

As if to compensate, Singleton goes burlesque, first with Angel's hoochie-mama girlfriend (Sofia Vergara) — surely the most annoying, ugly stereotype we've seen this year — and then with a comically abusive gangster (Chiwetel Ejiofor from “Dirty Pretty Things”) who makes his misbehaving minions eat off the floor like dogs. Why couldn't he just brain them with a baseball bat, like a regular underworld sociopath?

Singleton tries to keep us on our toes with the usual twists and secret allegiances, but it's a two-dimensional game, bereft of psychological contour. Sure, “Four Brothers” fires more bullets than “Man on Fire,” “The Limey” and other recent thrillers about wronged, rampaging men, but of a dramatically lower caliber.